Grinding machine



y 1963 N. s. HUMES ETAL 3,089,291

GRINDING MACHINE Filed Nov. 2, 1961 DER/CK A2 01/4152,

Hoey

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3,089,291 Patented May 14, 1963 3,089,291 GRINDING MACHINE Norman S. Homes, Worcester, and Frederick A. Hohler,

Holden, Mass, assignors to The Heald Machine Company, Worcester, Mass, av corporation of Delaware Filed Nov. 2, 1961, Ser. No. 149,754 7 Claims. (Cl. 51-103) This invention relates to a grinding machine and more particularly to apparatus arranged to finish a surface of revolution by the abrasion process, the expression abrasion including the processes of grinding and/ or burring.

In grinding operations it has been found that the rate of stock removal may be increased by increasing the pressure between the abrasive wheel and the workpiece; the limitation on this procedure is the breaking strength of the wheel. It is well known from theory and practice, furthermore, that a certain optimum relationship must exist between the speed of the wheel and the surface speed of the workpiece. Workpiece surface speeds present a problem, particularly in the case of the grinding of surfaces of revolution. For instance, in the grinding of internal bores, it is common practice to support the workpiece on an outside or external surface of revolution; such a situation exists, for instance, in the grinding of the internal bore of a bearing race, in which case the bearing race would be supported on the outside diameter. A particularly useful method of thus supporting the workpiece by its outside diameter is by the use of shoes whose curvature closely corresponds to the outside diameter of the workpiece. In such shoe-type centerless grinding, when one attempts to remove stock at the maximum rate allowable under the given wheel structure, the unit pressure of the outside surface of the workpiece on the supporting shoe becomes very great. At these surface speeds the ordinary shoe materials tend to gall the exterior surface of the workpiece and, for that reason, in the past this has been the limit of efficiency of the grinding machine. Furthermore, attempts to operate at greater efliciency with rigid shoe materials in the prior art machines has resulted in very poor finish and in chatter marks on the internal bore. These and other difliculties have been substantially reduced in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide a grinding machine having a novel manner of supporting a workpiece.

Another object of this invention is the provision of a shoe-type centerless internal grinding machine having workpiece supporting elements formed of an elastorner material which is not subject to abrasion.

A further object of the present invention is the provision of a grinding machine in which feeding of the wheel into the workpiece surface to be finished takes place by the controlled-force method and in which the grinding forces may be maintained at an optimum high value with a high surface speed of the workpiece relative to the workpiece supporting member without damage to the workpiece.

It is another object of the instant invention to provide an internal grinding machine in which the finish of the ground surface is very high and chatter is reduced to a minimum.

It is a further object of the invention to provide a grinding machine capable of a high rate of stock removal but at the same time providing a smoothly-finished surface with an absence of chatter marks.

A still further object of this invention is the provision of a shoe-type c'enterless internal grinding machine in which minor variations on the locating surface of the workpiece are absorbed by the supporting shoes.

It is a still further object of the present invention to provide a shoe-type centerless internal grinding machine in which means associated with the feed of the wheel into the workpiece maintains the grinding force at a constant predetermined value and means associated with the suppor ing shoes removes minor variations in the grinding force.

Another object of the invention is the provision of a grinding machine in which a first means maintains the grinding forces at a constant predetermined value and a second means removes minor variations of the grinding forces.

Another object of the invention is the provision of a grinding machine in which a regulation of wheel spindle deflection removes variations of grinding force and a defiection of the workpiece-supporting shoes removes minor variations in grinding force.

Another object of the invention is the provision of a grinding machine in which the natural resilience of the wheel spindle and a resilient workpiece support are used to maintain cut-ting speed at a maximum value with a minimum of marking of the locating surface and the surface to be finished of the workpiece and a maximum smoothness of finish of these surfaces.

With these and other objects in view, as will be app-arent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

The character of the invention, however, may be best understood by reference to one of its structural forms as illustrated by the accompanying drawings in which:

FIG. 1 is a somewhat schematic plan view of a grinding machine embodying the principles of the present invention;

FIG. 2 is an enlarged vertical sectional view of the grinding machine taken on the line -IIII of FIG. 1; and

FIG. 3 is a schematic view of important elements of the machine.

Referring first to "FIG. 1 wherein are best shown the general features of the invention, the grinding machine, indicated generally by the reference numeral 10, is shown finishing the internal surface or bore 11 of a workpiece 12. The grinding machine 10 is of the type shown and described in the patent of Hahn, No. 2,680,941, in which feed takes place by the so-called controlleddorce method, wherein the grinding force remains constant but the rate of feed varies. The machine is also provided for means for compensating for the bending or deflection of the wheel spindle at high forces.

In general, the machine consists of a workhead 13 and a wheelhead 14 mounted on a massive common base 15. The wheelhead is provided with a spindle 16 rotatably mounted therein and the spindle is provided at its outer end with an abrasive wheel 17. The spindle and wheel are rotated by a high-frequency electric motor within the wheelhead 14. The wheelhead is slidably mounted on rails 18 and 19 which are mounted on the upper surface 22 of a wheelhead platen 21. The platen is provided with a fiat undersur-face 23 which rests on the flat upper surface 24 of the base 15. The rails 18 and 19 are parallel to the axis of the portion of the spindle 16 which is mounted in bearings within the wheelhead and, in general, they extend in a longitudinal direction, i.e., parallel to the axis of the workpiece. The platen 21 is pivotally connected to the base 15 by means of a pin 25 located under the geometric center of the workpiece 12. The wheelhead 14 is moved longitudinally along the rails 18 and 19 by means of a hydraulic linear actuator 26 which connects it to the platen 21. The platen 21 is pivoted, on occasion, about the pin 25 by means of a hydraulic linear actuator 27. Mounted on the upper surface 24 of the base 15 are a pair of rails 23 and 29 extending transversely of the axis of the workpiece. Slidably carunderstood in view of the above description.

ried by these rails is a workhead table 31. The workhead carries a rotatable drive platen 32 which is provided at the rearward end with a pulley 33 driven by a belt 34 extending around a pulley 35 which is mounted on a motor 36, which, in turn, is mounted on the table 31. A diamond dressing unit 37 is also mounted on the upper surface of the table 31 as is a shoe support 38. The table 31 is moved over the rails 28 and 29 by means of a hydraulic linear actuator 47 which consists of a cylinder and piston at the outboard end of which is connected a hydraulic pump 48 which operates through a pressure regulating valve 49. A suitable hydraulic system, not shown, provides the actuators 2 6 and 27 with pressure fluid on occasion.

In FIG. 2 it can be seen that the workpiece 12 is of a generally annular form and is provided with an external cylindrical surface 39 and, as has been described, an internal bore 11. For the purposes of illustration, the workpiece is shown asthe outer race of a ball bearing. It will be understood that the external surface 3 has been finished in a previous operation but it is not, because of its ultimate use as the exterior of a roller bear- .ing race, ground to as fine a finish or as perfect an outof-round condition as is desirable for the internal bore 11.

The shoe support is provided with an upwardly-extending abutment 41 adapted to be located directly under the workpiece 12 and a laterally-extending abutment 42 adapted to be located behind the workpiece. The abutments 41 and 42 are provided with concentric cylindrical surfaces 43 and 44, respectively, in the manner taught in the patent of Blood, Reissue No. 24,202. Mounted on the surface 43 of the abutment 41 is a contact block 45 of resilient material, while a similar contact block 46 -is mounted on the surf-ace 44 of the abutment 4 2. The

contact blocks are attached to their respective cylindrical surfaces by cementing or other suitable means. The blocks are formed of an elastomer material of high abrasion resistance. A suitable material is the substance known as Disogrin, manufactured by the Disogrin Industries, Inc., which material isa solid polyurethane and consists of an interlaced poly addition product taken of both a polyester and a diisocyanate. This material has all of the elastic properties of rubber and similar materials, but has a very low coefficient of friction and has a very high resistance to abrasion. The particular grade of Disorgrin which has proved of particular usefulness is type 1DSA8655, which has a tensile strength of 5500 p.s.i., a durometer hardness (Shore scaleA) of 86, a modulus of elasticity 225 p.s.i., and an abrasive resistance around2' /2 to 4 times that of rubber.

The operation of the invention will now be readily First of all, the ,wheel 17 is rotated by means of the motor in the wheelhead 14. The motor 36 rotates andturns the drive platen 32 which, in turn, contacts the .end surface of the workpiece 12 and rotates it also. Various means (not shown) are used to press the workpiece axially against the drive platen; for instance, an outboard clamping plate may be used in accordance withthe patent to Menard, No. 2,951,320, or the platen may be magnetic to hold the workpiece in contact, as shown in the patent of Yingst, No. 2,933,862. In any case, the workpiece is rotated so that the external surface 39 slides over the contact blocks 45 and 46 on the shoe support 38. The actuator 26 is energized causing the wheelhead 14 to move toward the workpiece so that the wheel 17 enters the bore 11. Once the wheel is within the bore it is reciprocated axially within the bore in the usual way.

When thewheel 17 lies within the bore 11 and is reciprocating, the table 31 is moved forwardly and carries the workpiece 12 with it. This is accomplished by energization of the actuator 47 which, it will be recalled, is supplied with fluid whose pressure is very carefully regulated. Eventually, the workpiece comes into contact with the wheel 17 and the grinding pressure begins to build up. It will be understood that the force presented by the fiuid in the actuator 47 is balanced during grinding by the working pressure between the wheel 17 and the surface of the bore 11 of the workpiece; therefore, the grinding pressure builds up quickly to the predetermined value, remains at that value, and never exceeds it. As the grinding force builds up, the actuator 27 is energized to rotate the platen 21 about the pivot pin 25, thus inclining the axis of the spindle 16 to the axis of the workpiece. The amount of inclination is carefully selected so that, when the grinding forcereaches its .pre determined value, the bending or deflection of the spindle 16 will be a known amount; the inclination introduced by the actuator 27 will be sufficient so that, when the spindle 16 is bent, the wheel 17 resides within the bore with its axis parallel to theaxis of the workpiece. In other words, the generatrices of the wheel are-parallel to the generatrices of the bore 11; this assure that the bore, when it is ultimately finished, is a perfect right circular cylinder in the present example or, if the bore is to be tapered, that the taper is exactly the desired value. The grinding force is exactly balanced by the pressure in the hydraulic linear actuator 47. If there is a large variation of the pressure between the wheel and the workpiece (brought about, for instance, by an out-of-round condition on the rough bore), the controlled-force apparatus of the machine will automatically take care of it. The use of the present invention has resulted in a fine finish on the bore 11 and complete lack of chatter marks. It is felt that the reason for this effect lies in the fact that there is inherent resilience in the contact blocks 45 and 46 that permits them to give slightly when the grinding pressure rises by very slight amounts, as compared to the amounts which would be compensated for by the ordinary controlled-force apparatus of the machine.

The advantage in using controlled-force grinding is that the grinding force can be selected at a value just under the value which would destroy the wheel. It has been found, however, from both theory and practice that, when such large grinding forces are used, the wheel 17 must be rotated at a very high rate of speed which, as is well known in the grinding art, requires that the surface speed of the bore 11 of the workpiece also be speeded up. In a practical case, the most desirable surface speed of the exterior surface 39 over the supporting shoes is in the order of four times what would normally be used. The reason why the contact blocks 45 and 46 are able to permit such fast surface speeds is that'the coefiicient of friction of the material is very low; but surprisingly enough, the resistance to abrasion and wear is very high.

In FIG. 3 the schematic drawing will assist in an understanding of the machine operation. It can be seen there that the wheel 17 presses against the workpiece 12 and that the workpiece 12 is resiliently supported by a spring 51 which represents the inherent resilience of the blocks 45 and 46, the blocks themselves being connected ultimately at their other sides to the base 11 which is rigid. The wheel 17 is mounted on a cantilever spring consisting of the spindle 16, represented in the drawing by the spring 52 whose other end presses against the rigid base 11. The force P, which presses the two members together, represents the force brought about by the actuator 47 and is maintained at a constant value by the fact that the fluid pressure is regulated. It will be understood from an examination of the machine itself that the spring 51 is a very stiff spring, since the contact blocks 45 and 46, although they are constructed of elastomer material, are plate-like and thin in nature and will only move under pressure by small amounts and by high frequency variations in force. The spring '52 is a relatively soft spring, since the spindle 16 is a cantilever and has considerable natural resilience. It is contemplated that the gauging of-the machine be accomplished by the so-called 5. Siiematic method in which the diamond dressing unit 37 is -very carefully set and the wheel 17 is withdrawn from the bore just before the finishing operation is finished to pass over the diamond, to be'dressed, and then to return to the workpiece. It has been found that, in internal grinding machines of this kind, the fact that the workpiece is mounted on resilient shoes and the wheel itself is mounted on a resilient cantilever does not prevent accurate work from taking place, since the positions of the elements at the end of the grinding cycle are repeatable.

It has also been found that the out-ofround condition of the finished bore brought about by the practice of the present invention is considerably better than that of the rough external surface 39. This is explained by the belief that, when a protrusion of the out-of-ro-und condition strikes the contact blocks 45 and 46, the higher pressure forces set up thereby causes the blocks to be depressed or deflected so that the workpiece actually moves away from the wheel. The reason for the surface finish being so high is felt to reside in the fact that the contact blocks provide a resilient support of high natural frequency for the wrokpiece and this serves to smooth out any very minor variations in pressure between the wheel and the workpiece.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent is:

1. A grinding machine for finishing a workpiece having an external surface of revolution, comprising means for supporting the workpiece by contact with the external surface thereof, means for rotating the workpiece about the axis of the said surface, a wheelhead having a spindle and an abrasive wheel mounted on the spindle, means to bring about relative movement between the workhead and the wheelhead to bring about an abrading action between the wheel and the workpiece, and shoes associated with the supporting means and contacting the external surface of the wrokpiece, the said shoes being formed of an elastomer material of high abrasive resistance.

2. A grinding machine for finishing 'an internal surface of revolution in a workpiece having a generally cylindrical external surface, comprising a workhead for supporting the workpiece by contact with the external surface thereof and rotating it about the axis of the said internal surface, a wheelhead having a spindle and an abrasive wheel mounted on the spindle, means to bring about relative movement between the workhead and the wheelhead to bring about an abrading action between the wheel and the internal surface, means responsive to contact between the wheel and the workpiece to limit to a predetermined value the force with which the wheel is applied to the workpiece, and shoes associated with the workhead and contacting the external surface of the workpiece, the said shoes being formed of an elastomer material of high abrasive resistance.

3. A grinding machine for finishing a workpiece having an external surface of revolution, comprising means for supporting the workpiece by contact with the external surface thereof, means for rotating the workpiece about the axis of the said surface, a wheelhead having a spindle and an abrasive wheel mount-ed on the spindle, means to bring about relative movement between the workhead and the wheelhead to bring about an abrading action between the wheel and the workpiece, and shoes associated with the workhead and contacting the external surface of the workpiece, the said shoes being formed of an interlaced poly addition product taken of both a polyester and a diisocyanate of high abrasive resistance.

4. A grinding machine for finishing an internal surface of revolution in a workpiece having a generally cylindrical external surface, comprising a workhead for supporting the workpiece by contact with the external surface thereof and rotating it about the axis of the said internal surface a wheelhead having a spindle and an abrasive wheel mounted on the spindle, means to bring about relative movement between the workhead and the wheelhead to bring about an abrading action between the wheel and the internal surface, mean responsive to contact between the wheel and the workpiece to limit to a predetermined value the force with which the wheel is applied to the workpiece, and shoes associated with the workhead and contacting the external surface of the workpiece, the said shoes being formed of an interlaced poly addition product taken of both a polyester and a diisocyanate of high abrasive resistance.

5. A grinding machine for finishing an internal surface of revolution in a workpiece having a generally cylindrical external surface, comprising a workhead for supporting the workpiece by contact with the external surface thereof and rotating it about the axis of the said internal surface, a wheelhead having a spindle and an abrasive wheel mounted on the spindle, means to bring about relative movement between the workhead and the wheelhead to bring about an abrading action between the wheel and the internal surface, means responsive to contact between the wheel and the workpiece to limit to a predetermined value the force with which the wheel is applied to the workpiece, means inclining the wheelhead when the force is at the pre-determined value so that the surface of the wheel and the internal surface of the workpiece are parallel despite spindle deflection, and shoes associated with the workhead and contacting the external surface of the workpiece, the said shoes being formed of an elastomer material of high abrasive resistance consisting of a compound of a polyester and a diisocyanate.

6. A grinding machine for finishing an internal surface of revolution in a workpiece having a generally cylindrical external surface, comprising a workhead for supporting the workpiece by contact with the external surface thereof and rotating .it about the axis of the said internal surface, a wheelhead having a spindle and an abrasive wheel mounted on the spindle, means to bring about relative movement between the workhead and the wheelhead to bring about an abrading action between the wheel and the internal surface, means responsive to contact between the wheel and the workpiece to limit to a predetermined value the force with which the wheel is applied to the workpiece, and a workpiece support associated with the workhead, and shoes mounted on the support contacting the external surface of the workpiece, each shoe being formed of a thin block of an elastomer material of high abrasive resistance, one shoe being located directly under the workpiece and another being located away from the said one shoe.

7. A grinding machine for finishing an internal surface of revolution in a workpiece having a generally cylindrical external surface, comprising a workhead for supporting the workpiece by contact with the external surface thereof and rotating it about the axis of the said internal surface, a wheelhead having a spindle and an abrasive wheel mounted on the spindle, means to bring about relative movement between the workhead and the wheelhead to bring about an abrading action between the wheel and the internal surface, means responsive to contact between the wheel and the workpiece to limit to a predetermined value the force with which the wheel is applied to the workpiece, means inclining the wheelhead when the force is at the pre-determined value so that the surface of the wheel and the internal surface of the workpiece are parallel, despite spindle deflection, and a workpiece support associated with the workhead, and shoes mounted on the support contacting the external surface of the workpiece, ea'ch shoe being formed of a thin block of an elastomer material of high abrasive resistance consisting References Cited in the file of this patent UNITED STATES PATENTS Nor-ton Nov. 19, 1929 8 vvRiedling Mar. .2, Humes June 15, Hahn June 15, Cann June 17, Carlisle -Mar. 8, Cann Mar. 8, Lockwood May 8, 

1. A GRINDING MACHINE FOR FINISHING A WORKPIECE HAVING AN EXTERNAL SURFACE OF REVOLUTION, COMPRISING MEANS FOR SUPPORTING THE WORKPIECE BY CONTACT WITH THE EXTERNAL SURFACE THEREOF, MEANS FOR ROTATING THE WORKPIECE ABOUT THE AXIS OF THE SAID SURFACE, A WHEELHEAD HAVING A SPINDLE AND AN ABRASIVE WHEEL MOUNTED ON THE SPINDLE, MEANS TO BRING ABOUT RELATIVE MOVEMENT BETWEEN THE WORKHEAD AND THE WHEELHEAD TO BRING ABOUT AN ABRADING ACTION BETWEEN THE WHEEL AND THE WORKPIECE, AND SHOES ASSOCIATED WITH THE SUPPORTING MEANS AND CONTACTING THE EXTERNAL SURFACE OF THE WORKPIECE, THE SAID SHOES BEING FORMED OF AN ELASTOMER MATERIAL OF HIGH ABRASIVE RESISTANCE. 